1. Field of the Invention
The present invention relates to a white light emitting device emitting white light having excellent characteristics, and a display apparatus and an illumination apparatus using the same.
2. Description of the Related Art
In general, a wavelength conversion phosphor material is used to convert a particular wavelength of light from various light sources into a desired wavelength of light. In particular, a light emitting diode (LED), among various light sources, is able to be driven with low power consumption and has excellent light efficiency so it may be advantageously applied to an LED backlight, a vehicle lighting apparatus, and a home lighting apparatus. Recently, a phosphor material has been recognized as a core technology in the manufacturing of a white light emitting device.
In general, a white light emitting device is manufactured by applying one or more types of phosphor (e.g. red, yellow, or green phosphors) to a blue or an ultraviolet LED chip. In particular, in order to obtain desired natural white light, two or more phosphors, rather than a single phosphor (e.g. a yellow phosphor), may be mixed. For example, a red phosphor and one or more other phosphors may be mixed. In this case, if a full-width half-maximum (FWHM) of each of the phosphors is low, a sufficient color rendering index cannot be secured and there will be a limitation in implementing desired natural white light. The requirement of color rendering may be a critical evaluation item in employing the white light emitting device as a light source for illumination.
A silicate-based phosphor, which is generally advantageous in terms of FWHM characteristics, has relatively low thermal stability as compared with other phosphors, so it is not suitable for a phosphor of an LED device used in high temperature conditions. In particular, in the case of a blue LED chip, since a large amount of heat is generated therein, the use of a silicate-based phosphor having low thermal stability may be considerably problematic.
An nitrogen (N)-containing compound phosphor, such as a nitride-based phosphor, has relatively high thermal stability, but has a relatively low FWHM, and accordingly, the color reproducibility thereof may be low and desired color rendering properties may not be secured.